1. Field of the Invention
The present invention relates to a method and apparatus for the in situ treatment of acid mine drainage water or acidic drainage water from mine tailings in order to remove dissolved heavy metal ions and sulfate ions therefrom, and more specifically to a method and apparatus for the foregoing purpose utilizing sulfate reducing bacteria.
2. Statement of the Prior Art
Water flowing from mines percolates through tailings piles, and in the presence of oxygen from the air reacts with the metal sulfides contained in the tailings, such as iron pyrites or iron sulfides, forming soluble metal sulfates and sulfuric acid in the water stream leaving the mine tailings.
The use of sulfate reducing bacteria for producing hydrogen sulfide from a solution containing sulfate ions and metal ions, and the subsequent reaction of the hydrogen sulfide with the metal ions to remove the metal ions from the solution as solid metal sulfides, is an old and well-known process. See U.S. Pat. No. 5,587,079, issued Dec. 24, 1996, to M. V. Rowley, for "Process for Treating Solutions Containing Sulfate and Metal Ions." The chemical reactions involved in the process are described in detail in the Rowley et al. patent. The Rowley et al. patent describes and shows a bioreactor using sulfate reducing bacteria to convert sulfate ions to sulfide ions which in turn react with heavy metals ions in an aqueous solution to produce solid metal sulfides.